libc/uClibc: force use of ctor/dtor

Although ctor/dtor do not seem strictly required, missing them proves
rather inconvenient, as ld can't link binaries.

Reported-by: John Spencer <maillist-uclibc@barfooze.de> (sh4rm4 on IRC)
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # Blackfin specific configuration file

 ## select ARCH_SUPPORTS_32

 ## select ARCH_DEFAULT_32

 ## select ARCH_DEFAULT_LE

 ## select ARCH_SUPPORT_ARCH

 ## select ARCH_SUPPORT_CPU

 ## select ARCH_SUPPORT_TUNE

 ## select ARCH_SUPPORT_FPU

 ##

 ## help The Blackfin architecture